Black Mesa

It seems, wherever you go in this part of the world, you find a Black Mesa. It shouldn’t be surprising, really, when you consider the Rio Grande crosses an oblique line of volcanoes.

There are two in this area. North of town, the ten-mile long finger of land between the Rios Grande and Chama has been called the Black Mesa by geologists since George Wheeler named it so in 1876. Down on the San Ildefonso grant near the road that people use to commute between the valley and Los Alamos there’s another, rising 500' from the surrounding flat lands that slope to the river.

When I first moved here, I was told or read the San Ildefonso mesa was the cap of the Valles Grande volcano that had landed there when it erupted. I’ve also been told it was the last retreat of the pueblo peoples fighting Diego de Vargas in the entrada and that there’s a pair of peregrine falcons nesting there.

Ted Galusha and John Blick resolved the ambiguous naming problem by calling the San Ildefonso mesa the Round Mountain. I prefer to find another name for the peninsula of land, perhaps Wheeler’s Black Mesa or the Chamita Black Mesa.

They also dispelled any romantic notions about its origins.

It’s an independent cinder cone built around a volcanic neck that was formed some 4.4 million years ago in the early Pliocene, possibly as part of the Cerros del Rio volcanic field southeast of the Otowi bridge. According to Daniel Koning, one of its lava flows has been dated to about the time the Rio Grande was becoming a perennial river, long before the Toledo and Valle Grande eruptions.

The base is dark gray to black basalt. The top is covered with river cobbles and pebbles laid down about 1.5 million years ago, long before the lakes described by Steven Reneau and David Dethier.

Cinder cones are the simplest type of volcanos, central vents surrounded by fans of erupted debris. Volcanic necks are formed when the magma hardens within the volcano. Red cinders found on the southwest side suggest an eruption was through that side.

When water washes away the softer materials that surrounds a volcano, the basaltic blocks drop into a dense mass around the base that eventually prevents further erosion. If indeed this volcano was standing in 500' of water in the early Pleistocene, there was a great deal of water available to consolidate the current formation into a fortress which has since survived those lakes and, perhaps, created the fans where juniper now grow.

Top: Black mesa behind cottonwoods along the Rio Grande taken from the west side along route 30.
Bottom: Mesa taken from northeast; the ranch road wanders towards it after leaving the far arroyo.

Mastodons

The first time I heard of a mastodon I was sitting in a lecture hall at Michigan State listening to Russel B. Nye, who often combined cultural history with American literature.

I don’t remember what he said beyond a nearly complete skeleton found in Ohio had caused quite a sensation in the early nineteenth century. Somehow, I got the idea the skeleton was lying, fully exposed, on top of the ground and was stumbled upon much like the mounds had been.

I’ve since heard the animal was a glacier age mammal hunted by people using Clovis points. For some reason, that led me to think of them as great grass eaters.

When one’s interest in a subject is superficial, one’s knowledge tends to become a brew of facts, romantic legends and false conjectures.

I was, understandably, quite startled to find someone I think was Francis Klett say:

“In these beds, near Ildefonso, I made some excavations in 1873, while on the way to Fort Defiance under your expedition, (division 2,) and brought to light fossil bones of a mastodon, only one of them perfect, however; others were broken and yielded but fragments.”

The quotation is from the 1873 Annual Report of George’s Wheeler’s Geographical Surveys West of the 100th Meridian, and the location must be somewhere just north of route 502. That’s almost as close as the Otowi Bridge.

I suddenly needed to know more about mastodons. As I read, accretions of secretly hoarded facts dissolved.

It was true mastodons were glacial creatures and had been found in association with Clovis points.

However, they were associated with cold spruce woodlands, not grassland refuges.

Spruce growing where grass has been having a hard time surviving this year's drought.

Spruce near the Otowi bridge when those boulders blocked the Rio Grande creating lakes.

Spruce along those arroyos with the Qayi late-glacial sediments identified by Daniel Koning.

Spruce in my backyard. Who cares about a mastodon eating the foliage. Cold climate spruce right here where I’m writing.

Spruce.